Northwest coho do the “Jesus walk”

Streamwatchers in Seattle and Bellevue are reporting lots of salmon coming back to their humble waters.

I reported last week on fish returning to Piper’s, Thornton, Longfellow and Taylor creeks.

Just as the story ran, salmon began showing up at West Seattle’s Fauntleroy Creek, right out there by the Fauntleroy ferry and Lincoln Park. The stream has an outlet to the south of the ferry dock and there’s a platform nearby where visitors can watch the salmon climb the fish ladder. The first spawners were spotted Nov. 12 and by Friday Nov. 16, 69 fish were counted. They include coho and cutthroat trout.

While it’s really exciting to see these large fish flopping around in natural settings, some of their behavior can be a tad unnerving. For several years, researchers at NOAA Fisheries’ Northwest Fisheries Science Center have tracked coho returning to urban streams that die before spawning.

“We’ve seen it every year, in every stream we’ve been monitoring,” Nat Scholz, head of the research, recently told a crowd gathered for a salmon conference.

They exhibit unusual behavior, losing their orientation and equilibrium, mouths gaping and their fins splayed out. Part of that behavior includes the “Jesus walk” where the fish skitter across the water — check out videos here.

The cause of the pre-spawn mortality is uncertain. It affects coho, but not chum. It affects adult coho, but not juvenile coho (at least according to a newer study under way). The scientists have ruled out disease, pathogens, too-warm temperatures and too-low oxygen levels as potential causes.

The likely culprit is pollution that runs off roads and parking lots and roofs and landscaped gardens. The scientists have also made correlations between the amount of rain that has fallen and mortality rates (with the first rains, more pollution is coming off the roads) and with areas with more heavily used roads and mortality rates (both go up together).

The scientists are working to more specifically identify the cause of death. There are suspicions that it’s a combination of pollutants that alone would not be lethal to the fish, but that in combination trigger the neurologically odd behavior and death.